Waxes and hard fats have long been used to make candles. Wax has also been used since antiquity as a removable model in lost-wax casting of metals. Chemically, a wax is a type of lipid that comprises long-chain alkanes, esters, polyesters, and hydroxy esters of long-chain primary alcohols and fatty acids. More recently there have been developments where highly hydrogenated triglycerides have also been used as wax alternatives (e.g., U.S. Pat. Nos. 6,811,824; 6,890,982; and 7,267,743). There are different types of waxes: animal waxes (e.g., beeswax), vegetable waxes (e.g., soy wax, rice bran wax), mineral waxes (e.g., Montan wax), petroleum waxes (e.g., paraffin wax, microcrystalline wax), and synthetic waxes (e.g., polyethylene waxes, Fischer-Tropsch waxes). Specifically, paraffin waxes are hydrocarbons, mixtures of alkanes usually in a homologous series of chain lengths. They have been used to coat paper or cloth for water-resistant and stain-resistant functions. In the food industry, paraffin waxes have been utilized as sealants for containers, coatings for foods (e.g., candy, cheese), and food additives (e.g., chewing gum).
Vegetable oils are mostly extracted from plant seeds. In addition to edible vegetable oils, there are inedible types such as linseed oil, tung oil, and castor oil, which are used in lubricants, paints, cosmetics, pharmaceuticals, and certain industrial applications. Chemically, vegetable oils are considered as triesters of glycerin and typically contain fatty acids, monoglycerides, diglycerides, and triglycerides. To increase the melting point of vegetable oils, unsaturated vegetable oils are often transformed through partial or complete hydrogenation, a process wherein a double carbon bond is broken and two hydrogen atoms are added. If all double carbon bonds are eliminated by this process, it is called complete hydrogenation. As the hydrogenation process goes forward, the degree of saturation increases, the viscosity and the melting point of the oil also increase. The degree of hydrogenation is usually measured by the iodine value of the products. The lower the iodine value (IV), the higher the degree of hydrogenation, the higher the melting point.
A phenomenon in hydrogenating oils is that most of the hydrogenation occurs on the end fatty acids because the center arm of the triglyceride is shielded by the end fatty acids to some extent. This causes the resulting products to be more brittle. An example is a more spreadable margarine made from naturally more saturated oils than a margarine made from hydrogenated soy oil. Heavily hydrogenated vegetable oils with high melting point (>48° C. or 120° F.), vegetable waxes, have been used in such applications as candles, boxboard coatings and adhesives. However, these vegetable waxes are brittle because the degree of hydrogenation is high, resulting in hard waxes which tend to crack on flexing and are not suitable for applications such as flexible packaging and adhesives. Vegetable wax for candle-making is generally undesirable because the wax tends to crack on solidifying, which is aesthetically undesirable.
To overcome the deficiencies of low IV hydrogenated vegetable waxes, additives have been used to modify the waxes so that they are more flexible, less brittle with higher melting points. Compounds that have been added include mono- and diglycerides, vinyl polymers, petroleum and microcrystalline waxes, styrene butadiene polymers, fatty acids, alpha olefins, and glycerin. Petroleum oil or waxes can also be blended with vegetable or animal waxes/oils in order to modify their properties. Petroleum waxes are derived from crude oil processing, usually in the process of making lube oil. Synthetic waxes are also made using the Fischer Tropsch process which may involve hydrocracking of higher molecular weight materials into lower molecular weight waxes. Methods of hydrocracking are known to those experienced in the art. Petroleum oils and/or waxes are often hydrotreated when unsaturation of carbon-carbon double bonds is present in order to eliminate the double bond and make the oil or wax more stable. Hydrogen is also used to react with sulfur and or aromatic ring structures that may be present in the oil or wax mix in order to eliminate the sulfur and/or aromatic ring structures. Various catalysts including nickel, copper, various metal oxides and zeolites are often used in the hydrotreating, hydrodesulfurization and hydrocracking processes. But such modifications result in other problems such as (1) additives used to impart flexibility in candles have undesirable burning characteristics; (2) additives are often not renewable, leading to environmental concerns; and (3) additional mixing is required for the addition of additives, which increases manufacture cost and time. Therefore, there continues to be the need and the interest to develop an economic method to produce waxes of superior properties.